Electrical fires can quickly destroy a wind turbine and is the one of the leading causes of accidents in wind turbines. Wind turbines catch fire because highly flammable materials such as hydraulic oil and plastics are in close proximity to machinery and electrical wires. These can ignite a fire if they overheat or are faulty. Lots of oxygen, in the form of high winds, can quickly fan a fire inside a turbine. Once ignited, the chances of fighting the blaze are slim due to the height of the wind turbine and the remote locations that they are often in.
Main causes of fire ignition in wind turbines include electrical malfunction, mechanical failure, errors with maintenance and lightning strikes. For instance, a known problem is the production of stray shaft currents which may occur within the generators commonly used in wind turbines. The existence of large currents within a generator's bearings can lead to accelerated component wear and rapid failure. High-frequency currents, induced in the shaft of an induction generator through parasitic capacitive coupling, can reach levels of 60 amps and 1200 volts or greater.
Bearing damage has become a critical failure issue. If the bearings are oversized, they will last longer but the increase in friction reduces turbine efficiency. Smaller bearings allow for greater turbine efficiency but are more susceptible to overload conditions that can result in catastrophic destruction of the bearings.
In a wind turbine, a stator is directly connected to the grid, while a rotor is fed by an integrated gate bipolar transistor voltage-source inverter. The rotor-side converter regulates the electromagnetic torque and supplies part of the reactive power to maintain the constant voltage and frequency of the stator output. This arrangement makes operation at varying wind speeds possible while maintaining a constant stator voltage and a constant frequency output to the grid. The high-frequency switching introduces rotor-shaft voltages-exposing bearings, gearboxes, and other critical generator components to high-frequency currents. Inadequate generator-shaft grounding significantly increases the possibility of bearing damage. Without proper grounding, electrical discharges begin at start-up and grow progressively worse which causes concentrated pitting, friction and associated wear. Attached equipment, such as gearboxes, frequently end up with bearing damage of their own. Conductive grease is a common practice used to help bleed off harmful currents by providing a lower impedance path through the bearings, however, the conductive particles in the grease increase mechanical wear.
U.S. Pat. No. 7,096,965 discloses a method of proportioning a foam concentrate into a non-flammable liquid to form a foam concentrate/liquid mixture and create a flowing stream of the foam concentrate/liquid mixture. Nitrogen is introduced into the stream of the foam/liquid mixture to initiate the formation of a nitrogen expanded foam fire suppressant. The apparatus of this invention is adapted for expanding and dispensing foam and includes a housing defining an interior through which extends a discharge line.
U.S. Pat. Nos. 7,096,965 and 7,104,336 discloses a method and apparatus for proportioning foam concentrate into a non-flammable liquid to form a foam concentrate/liquid mixture.
U.S. Pat. No. 5,989,446 discloses a water additive for use in fire extinguishing and prevention. The additive comprises a cross-linked water-swellable polymer in a water/oil emulsion. The polymer particles are dispersed in an oil emulsion wherein the polymer particles are contained within discrete water “droplets” within the oil.
U.S. Pat. No. 5,190,110 discloses the fighting of fires or protection of objects from fire by applying water which comprises dispersing in the water particles of a cross-linked, water-insoluble, but highly water-swellable, acrylic acid derivative polymer in an amount sufficient to raise the viscosity.
U.S. Pat. No. 5,849,210 discloses a method of preventing or retarding a combustible object from burning including the steps of mixing water with a super absorbent polymer (“SAP”) to form one at least partially hydrated SAP, and applying the at least partially hydrated SAP to the combustible object, before or after combustion.
What is needed in the art is a system for use with wind turbines that can be used to stop a fire before it takes hold or gets out of control.